This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Members of the Moraxella genus are gram-negative, aerobic bacteria that have been isolated from a variety of mammalian hosts. During a survey of bacteria that colonize the nasopharynx of rhesus macaques, isolates of the Moraxella genus, identified as M. catarrhalis, were observed in the majority of animals with demonstrated epistaxis, or "bloody nose syndrome." Several isolates from this survey were cryopreserved at the Tulane National Primate Research Center. One isolate was also obtained from an epistatic cynomolgus macaque at the U.S. Army Medical Research Institute of Infectious Diseases. Based on differences between the colony and gram stain morphology of rhesus isolates compared to that of human M. catarrhalis isolates, we hypothesized that the nonhuman primate Moraxella might be unique. These isolates were reassessed by multiple parameters. Despite differences in cell and colony morphology, the rhesus isolates, by each biochemical test, were identical to M. catarrhalis and not other human Moraxella subspecies. Biochemical analysis of the cynomolgus isolate by Vitek 2 compact (St Louis, Mo) revealed that it belonged to a Moraxella group, but could not differentiate between species. However, sequencing of the 16S ribosomal RNA gene from four representative rhesus isolates and the cynomolgus isolate showed closest homology to Moraxella lincolnii, a human respiratory tract inhabitant, with 90.16% identity. In order to examine rhesus macaques as potential hosts for M. catarrhalis, a total of eight animals were inoculated with human isolates of this strain. Only one of the animals was colonized and showed disease, whereas four of four macaques became epistatic after inoculation with the rhesus Moraxella isolate. Thus, this nasopharyngeal Moraxella species is a previously uncharacterized, distinct pathogen of nonhuman primates. It is not M. catarrhalis.